Weighing apparatus with means for correcting effects of vibrations

Abstract

A weighing apparatus has a scale cell and a dummy cell, both similarly structured and cantilevered. A load to be measured is applied to the free end of the scale cell and a standard weight is attached to the free end of the dummy cell. Analog electrical signals from these cells are converted to digital data. The effect of the standard weight is removed from the digital data from the dummy cell to obtain the effect of external vibrations which effect is multiplied by a suitable coefficient dependent on the applied load and subtracted from the digital data from the scale cell.

What is claimed is: 
     
       1. A weighing apparatus comprising a base,   a weight-measuring load cell having one end thereof secured to said base and the other end thereof supporting a load-carrying table,   a dummy load cell having one end thereof secured to said base, a standard weight being attached to the other end of said dummy cell,   first analog-to-digital converter means for converting analog electrical signals from said weight-measuring load cell to digital data,   first filter means for filtering digital data from said first analog-to-digital converter means,   second analog-to-digital converter means for converting analog electrical signals from said dummy load cell to digital data,   second filter means for filtering digital data from said second analog-to-digital converter means,   multiplier means for multiplying a coefficient to output data from said second filter means, said coefficient being dependent on the weight of an object being weighed by said weighing apparatus, and   subtractor means for outputting the difference between data outputted from said first filter means and an output from said multiplier means.   
     
     
       2. The weighing apparatus of claim 1 wherein said coefficient is proportional to said weight. 
     
     
       3. A weighing apparatus comprising a base,   a weight-measuring load cell having one end thereof secured to said base and the other end thereof supporting a load-carrying table,   a dummy load cell having one end thereof secured to said base, a standard weight being attached to the other end of said dummy cell,   signal multiplexing means for alternately outputting signals from said weight-measuring load cell and said dummy load cell at a multiplexing frequency which is shorter than external vibration frequencies,   analog-to-digital converter means for converting signals outputted from said signal multiplexing means to digital data,   filtering means for filtering digital data from said analog-to-digital converter means at said multiplexing frequency,   multiplier means for multiplying a coefficient to data outputted from said filter means when said signal multiplexing means is outputting a signal from said dummy load cell, said coefficient being dependent on the weight of an object being weighed by said weighing apparatus, and   subtractor means for outputting the difference between data outputted from said filter means when said signal multiplexing means is outputting a signal from said weight-measuring load cell and data from said multiplier means.   
     
     
       4. The weighing apparatus of claim 3 wherein said coefficient is proportional to said weight. 
     
     
       5. A weighing apparatus comprising a base,   a weight-measuring load cell having one end thereof secured to said base and the other end thereof supporting a load-carrying table,   a dummy load cell having one end thereof secured to said base, a standard weight being attached to the other end of said dummy cell,   signal multiplexing means for alternately outputting signals from said weight-measuring load cell and said dummy load cell at a multiplexing frequency which is shorter than external vibration frequencies,   a common preamplifier means for receiving outputs from said signal multiplexing means,   analog-to-digital converter means for converting outputs from said preamplifier means to digital data,   filter means for filtering digital signals from said analog-to-digital converter means at said multiplexing frequency,   multiplier means for multiplying a coefficient to data outputted from said filter means when said signal multiplexing means is outputting a signal from said dummy load cell, said coefficient being dependent on the weight of an object being weighed by said weighing apparatus, and   subtractor means for outputting the difference between data outputted from said filter means when said signal multiplexing means is outputting a signal from said weight-measuring load cell and data from said multiplier means.   
     
     
       6. The weighing apparatus of claim 5 wherein said coefficient is proportional to said weight.